Everyday examples of the Joule the energy required to lift a small apple one meter straight up. the energy released when that same apple falls one meter to the ground. the energy released as heat by a quiet person, every hundredth of a second. the energy required to heat one gram of dry, cool air by 1 degree Celsius. one hundredth of the energy a person can receive by drinking a drop of beer. the kinetic energy of an adult human moving a distance of about a hand-span every second.

Power Power: the rate at which work is performed – Or, the rate at which energy is transmitted – Or the amount of energy expended per unit time Measured in Watts: Other units: – HP or horse power – BTUs

Horse power Arose as a result of the invention of the steam engine. People needed a way to compare the power of a steam engine to that of the horses it was replacing. Confusing unit there are too many different definitions!

BTU BTU: British Thermal Units - an energy unit – the amount of heat required to raise the temperature of one pound of liquid water by one degree from 60° to 61°Fahrenheit at a constant pressure of one atmosphere Used in the power, steam generation, heating and air conditioning industries and the energy content of fuels. However, BTU is often used as a unit of power, where BTU/hour is often abbreviated BTU. – So you need to watch the context!

Back to Watts….. A human climbing a flight of stairs is doing work at a rate of about 200 watts. A typical household incandescent light bulb uses electrical energy at a rate of 25 to 100 watts, while compact fluorescent lights typically consume 5 to 30 watts. A 100 Watt light bulb consumes energy at the rate of 100 joules/second. After 1 hour, this light bulb uses 100 watt-hours 1 kilowatt (kw) is 1000 Watts

Examples In a certain room in your house, you use a 100 W light bulb. This light is on for 5 hours every day. How much energy does it use? 1 W = 1 J/s and there are 5h x 60min/hour x 60 sec/min = 18,000s in 5 hours so the total energy used is 100 j/s *18000s = 1.8 x 10 6 J. Lets assume the same lighting level can be achieved using a 30 W compact florescent bulb. How much energy is used by the compact florescent bulb?

Examples Total energy = 30 j/s x s = 5.4 x 10 5 j. So how much energy is saved every day using the compact florescent bulb? Take the difference between the energy used by the two different light bulbs: 1.8 x 10 6 j x 10 5 j = 1.3 x10 6 j. Lets look at this in something you might be able to relate to better than joules---dollars!

Example continued After 5 hours, our 100 W light bulb uses 500 Watt-hours, or 0.5 Kwh. The 30 W bulb will use 150 Watt hours or 0.15 Kwh. Assume electricity costs 11 cents/Kwh (average cost in the US in April 2008). So it costs.5 KwH x 11 cents/Kwh = 5.5 cents every day to run the 100 W light bulb and 0.15Kwh x 11 cents = 1.65 cents every day to run the compact florescent.

Example continued So in a year, the 100 W light bulb costs you 5.5 cents/day X 365 days/year = $20.00 and the 30 W bulb costs costs you 1.65 cents/day x 365 days/year = $5.50.

Types of Energy: kinetic and potential Energy Kinetic energy - energy of a moving object KE=1/2mv 2 Potential Energy – Energy stored in a system, for example an object of mass m, a distance h above the surface of the earth has a potential energy given by mgh. g is the acceleration due to gravity = 9.8 m/s 2

More examples of potential energy Another example is a spring, compressed a distance x from its equilibrium point has a potential energy 1/2kx 2, where k is the spring constant, a property of the spring.

Chemical Energy Energy that is released via chemical reactions. Often times release is through combustion such as energy generation via coal Another example is a battery

Heat Energy Temperature Scales: Fahrenheit – based on the height of liquid (often mercury or alcohol) in a glass tube. Celsius – another scale using height of liquid in a tube Kelvin-absolute scale – True measure of energy Energy associated with the random motions of the molecules in a medium. Measured by temperature

Fahrenheit temperature scale Freezing point of water set at 32 and boiling point set at 212, so there is 180 degrees between them and each degree is 1/180 of the difference between these two points.

Celsius temperature scale Freezing point of water set at 0 and boiling point set at 100, so there is 100 degrees between them and each degree is 1/100 of the difference between these two points.

Kelvin temperature scale O k is absolute zero. All molecular motion stops. Interval set so that 1 k = 1 c So to convert from c to k k=c+273

Mass Energy E = mc 2 Energy and mass are equivalent C = 3 x 10 8 m/s. A big number and its squared! So even if m is small, E is big. A small mass, converted to energy, gives a lot of energy!

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